In a pyrotechnic inflator, inflation gas generated by combusting gas generating charge is hot and contains residuals. Conventionally, a generally cylindrical, mesh filter is provided on the outer circumference of the combustion chamber for cooling the inflation gas and removing the residuals. However, the filter is made of metal and therefore can be heavy and bulky. From the viewpoint of lightening and downsizing of the metal inflator, it is preferable to reduce the capacity of the filter. Prior art (for example, Patent Literature 1) discloses an inflator having a combustion chamber that houses gas generating charge and is provided with numerous gas outlet ports that allow exit of inflation gas, all along the circumference of the combustion chamber, a generally cylindrical bulkhead that is located around the combustion chamber to provide detour of inflation gas, and generally donut-shaped plate filters located on opposite ends in the axial direction of the bulkhead such that the inflation gas exited the gas outlet ports of the combustion chamber is cooled off while taking a roundabout path by the bulkhead and passing through the filters and exits to an exterior from gas discharge ports formed outside of the bulkhead.
To enhance lightening and downsizing of the inflator, it is desired to dispense with a filter. In response to such a demand, Patent Literature 2 and 3, by way of example, disclose a filterless inflator: the inflator includes an inner case which houses gas generating charge and an outer case located on the outer circumference in a circumferential direction of the inner case. The outer case includes a gas guide portion that has a zigzag shaped section when taken along an axial direction of the inflator and is provided on the outer end remote from the inner case with a gas discharge port which allows exit of inflation gas to an exterior of the inflator. In operation of this filterless inflator, a guide plane located on the inner circumference of the gas guide portion cools hot inflation gas exited gas outlet ports on the inner case and catches residuals while the gas hits the guide plane and is deflected by the guide plane, and then the gas exits to an exterior from the gas discharge ports of the gas guide portion.    Patent Literature 1: JP2007-131254    Patent Literature 2: Japanese Utility Model Registration No. 3122258    Patent Literature 3: Japanese Utility Model Registration No. 3122259